In a data or command communication system it may be desirable to conduct a communication at low rate by using a transmission spread spectrum. This makes it possible to optimise the resistance of the communication system to different disruptors. The communication system can preferably be based on a “chirp” type spread spectrum modulation. The chirp signal is by definition a pseudo-periodic signal modulated in frequency around a carrier frequency. In general, the frequency of this chirp signal varies linearly in relation to the carrier frequency between a low value and a high value of the frequency band. A first half-cycle of this signal can be a positive slope of linear frequency variation, whereas a successive second half-cycle of this signal can be with a negative slope of linear frequency variation.
The patent application US 2014/0064337 A1, which describes a process for synchronisation of a receiver on the base of a chirp signal transmitted by a transmitter, can be cited in this context. The clock signal of the receiver has to be synchronised initially with the clock signal of the transmitter to perform a data communication. To achieve this, the receiver captures the chirp signal from the transmitter. The receiver is configured to receive a chirp signal with at least one first frequency variation gradient in a half-cycle having an amplitude higher than 1. The receiver comprises a correlator suitable for correlating the first frequency variation gradient of the chirp signal with a first expected chirp signal to produce a first set of correlation results. At least one first correlation peak above the other correlation peaks is determined to be able to estimate the frequency and/or phase deviation. An adjustment unit is also provided to correct the phase and frequency of the first chirp signal of the receiver and thus be synchronised with the transmitter. However, the receiver does not perform a discrete Fourier transform (or DFT) of the sampled intermediate signal to enable the frequency or phase deviations to be found quickly. Therefore, this constitutes a disadvantage in enabling synchronisation to be made easier and the general consumption of the receiver to be reduced.